A photolithography process, transferring patterns on a mask to a substrate by an exposure process, is a important process of the semiconductor manufacturing technology. The photolithography process is a core step in the manufacturing of large scale integrations (LSIs). The complex and time-consuming photolithography processes of the semiconductor manufacturing are mainly performed by corresponding exposure apparatus. Further, the development of the photolithography technology or the improvement of the exposure apparatus are mainly focused on three factors: feature size, overlay resolution, and yield.
In the manufacturing of a semiconductor device, the photolithography process may include three main steps: changing wafers on the wafer stages; aligning the wafers on the wafer stages; and transferring patterns on the mask to the wafers. These three steps may be sequentially repeated on the same wafer stage.
Since the photolithography process is a key step of the semiconductor manufacturing process, how to improve the yield of an exposure apparatus in the practical manufacturing process has become a very important topic. Various exposure apparatus with twin-stages have been developed in past a few years in order to further increase the yield of the exposure apparatuses. The exposure apparatus with twin-stages may refer that when one wafer stage is performing an exposure, the other wafer stage may perform wafer alignment simultaneously, thus the wafer waiting time may be reduced; and the exposure efficiency of the exposure apparatus may be improved.
Another more advanced exposure apparatus is a cylindrical reticle system. The cylindrical reticle system may include a base and a wafer stage group for holding wafers on the base. The wafer stage group may include a plurality of wafer stages moving between a first position and a second position in a circular manner. Further, the cylindrical reticle system may include an alignment detection unit configured above the first position of the base. The alignment detection unit may be utilized to detect stage fiducials on the wafer stage at the first position and the alignment marks on a wafer on the wafer stage at the first position to align the wafer. Further, the cylindrical reticle system may also include a recticle stage on the second position of the base configured to hold a cylindrical reticle, and cause the cylindrical reticle to rate around a central axis of the reticle stage. The cylindrical reticle may be a hollow cylinder, and may have an imaging area and non-imaging areas at both sides of the imaging area. Further, the cylindrical reticle system may also include an illuminator box locating in the hollow cylindrical reticle to irradiate light through imaging area. Further, the cylindrical reticle system may also include an optical projection unit (lens) between the reticle stage and the base. The optical projection unit may be utilized to project the light passing through the imaging area of the cylindrical reticle onto an exposure region on the wafer on the wafer stage. When the wafer on the wafer stage moves from the first position to the second position and performs a unidirectional scan along a scan direction, the cylindrical reticle stage may rotate around the central axis for one cycle, the light passing through the imaging area of the cylindrical reticle may be projected onto the wafer on one wafer stage; and a column of exposure regions of the wafer along the scanning direction may be exposed.
The imaging area of the cylindrical reticle may include transparent regions and opaque regions; and the transparent regions and the opaque regions may form mask patterns. When an exposure light irradiates the imaging area of the cylindrical reticle, the light passing through the transparent regions may be projected onto the photoresist layer on the wafer, thus patterns corresponding to the mask patterns on the cylindrical reticle may be formed in the photoresist layer on the wafer.
The opaque regions of the imaging area of the cylindrical retile are usually formed by forming an opaque material layer on the imaging area, followed by etching the opaque material layer. When the opaque material layer is etched, a photoresist layer may often be formed on the opaque material layer. The photoresist layer may also be formed on the non-imaging areas of the cylindrical reticle. The photoresist layer formed on the non-imaging areas may contaminate the wafer stages of the cylindrical reticle apparatus. Thus, it may need a method to completely remove the photoresist layer formed on the end edges of the cylindrical retile.
FIG. 1 illustrates a cylindrical reticle having a photoresist layer. As shown in FIG. 1, the cylindrical reticle 104 includes a middle imaging area 43 and two non-imaging areas 41 at both sides of the imaging area 43. After forming a photoresist layer 109 on the cylindrical recticle 104, the imaging area 43 of the cylindrical reticle 104 is covered by the photoresist layer 109. The non-imaging areas 41 and side surfaces 31 of the cylindrical reticle 104 are also partially or completely covered by the photoresist layer 109. In order to form patterns on the cylindrical reticle 104, an exposure process is needed to expose the photoresist layer 109 on the imaging area 43 of the cylindrical reticle 104. Before performing the exposure process, the cylindrical reticle 104 having the photoresist layer 109 has to be installed in the reticle stage of a photolithography apparatus. The photoresist layer 109 on both end edges of the non-imaging areas 41 (may be referred as edge beads) and side surfaces 31 of the cylindrical reticle 104 may contaminate the reticle stage of the photolithography apparatus. Thus, the alignment of the cylindrical reticle 104 may be affected, and the particle contaminations of the photolithography apparatus may be beyond the desired requirements. The disclosed device structures, methods and systems are directed to solve one or more problems set forth above and other problems.